1. Field of the Invention
This invention relates to equipment security system for providing an alarm, namely, a visual and/or audible indication in response to any variation or modification of the condition of an equipment resulting from unauthorized removal of the equipment at a protected area.
2. Description of the Prior Art
It is often desirable, especially in an educational and research institute, to provide security to all circuit boards, micro-computers, terminals, peripheral devices, printers, etc. and yet at the same time provide sufficient flexibility to the users, such that the equipment may be movable and replaceable in order to meet the research requirements of the users. Hence, there is a need to provide an equipment security system whereby security could be provided to discourage unauthorized removal of the equipment and while not frustrating the user in normal application.
Various alarm systems are now known. However, many of these alarm systems suffer from a major problem in that a skillful intruder generally is able to defeat the alarm system and render it inoperative by shorting the condition sensing switches or the wires connecting the switches in a circuit. Another problem associated with sensor detector type security systems is that such systems would become inoperative because the metal body of the equipment may cause interference to the operation of the sensors. Other problems associated with the general type alarm systems is that such systems generally provide little flexibility to the users of the equipment. Hence, such systems are impractical in an educational, research environment.
In U.S. Pat. No. 4,524,349 to Hyatt, issued June 18, 1985, a security system is described using a microprocessor as a control means. The micro-processor is used to monitor the loop circuits, the generation of detector signals and the control of the alarm circuits. This security system is a complicated system and has many circuit components. Also, such system relates to an intrusion security system, flexibility may not be a prime consideration. Hence, such system may not be adopted successfully in an educational, research environment.
In U.S. Pat. No. 4,118,700 to Lenihan, issued Oct. 3, 1978, a security system is disclosed, having a single sensor loop having a plurality of detectors connected in a series, such detectors being connected in parallel with resistors of different value in order to identify the detectors. A "NAND" logic is used as an analog to digital converter having a digital detection signal output. This analog-to-digital converter having a single analog input and a plurality of comparators, is complicated and has many circuit components. Also, the Lenihan invention teaches a security system having a large number of detectors for detecting different conditions, such as smoke, fire or intrusion; hence such system would not provide the type of flexibility to the equipment users. Thus, it would not be suitable in an educational, research environment. As well, the equipment under monitor, when in operation may cause interference to the operation of the sensors or detectors. Thus, may cause unpredictable results to the security system.
U.S. Pat. No. 4,348,661 to Lucchesi, issued Sept. 7, 1982 teaches an alarm system providing improvements over the conventional bridge type alarm system. It uses operational amplifiers to detect open and/or short circuit conditions. Hence, the improvement removes the use of a complex circuit arrangement usually found in the conventional bridge type alarm systems. However, the Lucchesi system relates to a conventional burglar alarm environment for monitoring unauthorized intrusion. Hence, it would not provide the flexibility for equipment security purposes in an educational institute.
U.S. Pat. No. 4,065,762 to Walter, issued Dec. 27, 1977, teaches the use of an AC bridge instead of the conventional DC bridge for the comparator circuit in an alarm system. Such improvement introduces further security to the system in that it is much more difficult to match an AC voltage than a DC voltage in terms of phase angle between the voltage and current in an AC circuit. However, the Walter system does not provide equipment security means, and flexibility may be difficult to achieve in an AC bridge alarm system in that the connecting cable may pick up interference signals. As well, the AC current may cause interference to the operation of the equipment being monitored. In order to avoid the interference problem, complex shielding means may be necessary.
Canadian Pat. No. 1,130,885 to Dray, issued Aug. 31, 1982, discloses an AC bridge intrusion security system having reference and/or compensating elements. Again, this type of intrusion security system may not be useful in an educational institute and compensating elements may not be necessary since the equipment being monitored will be indoors and not subject to environmental changes.